As is known in the art, in modern automotive engine evaporation (EVAP) emission control systems, a carbon canister is required to adsorb and store fuel vapor to avoid atmospheric pollution. The canister operation involves two major modes—a loading mode and a purging mode. During the purging mode, fresh air enters the carbon canister to clean up the fuel vapor stored in it. In order to prevent dust contaminants entering the canister, an air filter is required at the entrance to the fresh air intake port. To detect EVAP leakage a diaphragm type natural vacuum leak detection (NVLD) device is installed in the EVAP system and is located between the air filter and the carbon canister. In order to protect the NVLD from the dust and water, a fine air filter is used. For such fine filter, exposure to water may reduce its performance and may even damage it.